arm64: dts: Add ARM SP805 watchdog DT node for NS2

We have one ARM SP805 watchdog instance on NS2 for non-secure software
hence this patch adds appropriate watchdog DT node in NS2 DT.

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Pramod KUMAR <pramodku@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>